Liquid crystal displays (“LCDs”) contain a backlight, which is the source of light that enables the LCDs to display images and texts. The liquid crystal that is in the display acts as a shutter to let the light through or not based on the command that is delivered by a corresponding control chip. Most LCDs use a cold cathode fluorescent light (“CCFL”) tube as the light source. CCFL is on all the time when the LCD is turned on. The video signal, or the content, or the image that is shown on the LCD is created by the controlling the orientation of the liquid crystal elements in the display panel.
The special glass panel of the LCD creates the colors based on the light filtering mechanism of the films on the glass panel. The light that is generated by the CCFL is white light in most of the LCDs, which is provided behind the glass panel, where the front side is the side of the viewer.
CCFL is energy efficient. However due to the use of hazardous materials in CCFL, the industry is phasing out CCFL from the backlight application. Also the CCFL-based backlight is kept turned on continuously even if no image is displayed. Furthermore the light is slow to turn on or off, thus it is difficult to switch it on or off based on the image.
However, it would be desirable to turn the backlight off if no image is being displayed, or for dark scene, or for a dark image. This would save energy, which would be especially beneficial for battery operated portable products. Furthermore the CCFL backlight lights the back of the whole display and has difficulty in providing zone backlighting, or fractional backlighting based on the image to be displayed. Namely if on one side of the display the image is a dark image, then that side does not need the backlight on. With CCFL technology, it is difficult to only light the needed area or zone, and especially at video image rates (30 to 60 frames a second) since CCFL cannot be turned on or off at fast rates.
Alternatively the industry has been embracing the use of white light emitting diodes, (“LEDs”) for backlights. Rather than having a CCFL light bulb, one uses a plurality of LEDs as the light source. However this solution is more costly than present CCFL backlights. The LED backlighting is also less energy efficient than the CCFL light source. Also the present so-called “white LEDs” do not emit pure white light, nor is it as white as the CCFL based backlight. Namely the white color is not truly optically white thus the resultant color quality of the image is poor. This LED solution might be adequate for LCDs for simple telephones, or instruments that do not need to display color pictures, or video, or television, (“TV”) programs. However for LCD for color TVs, video displays, and for color imagery, a better solution is needed.
With this need the industry has resorted to the use of RGB LED technology, namely LEDs with the three distinct colors, red green and blue (similar to the RGB concept in the CRT color TVs). According to color physics, one can generate for the human eye, the colors of the spectrum with the combinations of RGB. For example, white is created by turning on the three colors at the desired intensity, the red green and blue, which then appears to the eye as white. These techniques are well known for persons trained in the art, from the early days of CRT based color TV and color art graphics.